1. Field of the Invention
The invention relates to a catalytic reactor for catalytic conversion of exhaust gases, in particular for catalytic conversion of exhaust gases from internal combustion engines.
A catalytic reactor for emission control, in particular for motor vehicle engines, which is known from German Utility Model G 87 12 267.7 U1, is provided with a honeycomb body in which flow channels for exhaust gas are formed. The honeycomb body is disposed in a sleeve-like casing. Heat insulation is provided between the honeycomb body and an inner surface of the casing, so that during operation the casing cannot become too hot. German Utility Model G 87 12 267.7 U1 further proposes to provide the casing with an external insulating shell for heat insulation. Excessively large thermal gradients between the casing and the honeycomb body are prevented and surrounding components are protected from heat through the use of those measures.
A catalytic reactor which is known from European Patent 0 229 352 B1, corresponding to U.S. Pat. No. 4,713,361, is provided with internal and external insulation. Heat radiation towards the outside is reduced through the use of that measure.
The catalytic conversion of exhaust gases takes place above a temperature of 300.degree. C. If the catalytic reactor has not yet reached that temperature, the exhaust gas flows through the reactor without the desired conversion of the exhaust gas into harmless components taking place.
Different proposals have already been made for reaching the temperature at which the catalytic conversion begins as quickly as possible. The starting point of those proposals is the goal of heating up the catalytic converter as quickly as possible. For that reason, it has been proposed to use a pre-catalyst, the mass of which is relatively small as compared to the main catalytic converter. On the other hand, it has also been proposed to construct heatable catalytic converters, as is seen in the SAE Technical Paper 940470 entitled "Heating Catalytic Converter Competing Technologies to Meet LEV Emission Standards" by P. Langen et al.
A catalytic reactor for catalytic conversion of exhaust gases, in particular for exhaust gases of internal combustion engines, is known from U.S. Pat. No. 5,278,125. The reactor includes a honeycomb body provided with a large number of channels through which the exhaust gases can flow. The honeycomb body has a gas inlet side and a gas outlet side. The honeycomb body is thermally insulated from the gas inlet side onward over part of its length with respect to an internal casing in the housing of a casing. The required temperature is reached quickly in a front area of the honeycomb body through the use of the thermal insulation.